1. Field of the Invention
This invention relates to resin-impregnated filament wound pipe produced on a mandrel.
2. Background
Filament wound pipe able to withstand high pressures of a constant or intermittent nature are currently made by winding either resin-free or resin-impregnated filaments, such as glass, oriented asbestos, oriented organic fibers, graphite or carbon fibers, etc., at a uniform pitch or angle around a mandrel. It is known that it is important to maintain a uniformity in pitch for each layer of windings because the distribution of stresses critically hinges thereon.
In order to ensure uniformity of pitch for windings within each layer, a wind-stop is often employed. A "wind-stop" is herein defined to mean that location at which the angle of windings changes during the process of winding filaments or roving onto a mandrel. The angle of winding usually changes between layers where one layer is wound relative to the mandrel in a first direction and the next layer is wound relative to the mandrel in the opposite direction. Some examples of wind-stops are: a place where the diameter of a mandrel changes giving rise to a groove or a step, a row of peg-like projections which can be removed, expandable and retractable projections, and the like.
Examples of machinery and methods commonly used to manufacture filament wound pipe can be found in McLarty, U.S. Pat. No. 3,874,329 (1975) and McLarty et al., U.S. Pat. No. 3,629,028 (1971), both incorporated herein by reference.
Some of the resins used in filament wound pipe are thermosetting polyesters, phenolic resins, silicones, polyamides, melamine-formaldehydes, bisphenol A-epichlorohydrin and other epoxy resins and the like.
In the case of many thermosetting resins, there is a decrease in volume upon curing. This decrease in volume in the axial direction of a filament wound pipe can be as high as 5 percent. Any decrease in volume during cure will generally introduce stresses in the longitudinal or axial direction of a pipe which uses wind-stops to aid changes in the angle of wound filaments.